Method for fabricating a device with flexible substrate and method for stripping flexible-substrate

ABSTRACT

A method for fabricating a device with flexible substrate includes providing a rigid substrate. Then, a flexible substrate layer is directly formed on the rigid substrate, wherein the flexible substrate layer fully contacts the rigid substrate and a contact interface is formed. A device structure is formed on the flexible substrate layer. Alternatively, an interfacing layer can be formed on the rigid substrate and then the flexible substrate layer is directly formed on the interfacing layer. Thus, the flexible substrate layer can be stripped from the rigid substrate under a condition substantially without stress.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 94131431, filed on Sep. 13, 2005. All disclosure of theTaiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method for fabricating a device witha flexible substrate. More particularly, the present invention relatesto a method for fabricating a device with flexible substrate, which canalso be easily stripped from the rigid substrate.

2. Description of Related Art

As well known, an electronic product includes a lot of electronicdevices, such as transistor device. These electronic devices are usuallyformed on a substrate. Taking the conventional technology insemiconductor fabrication as the example, usually, a silicon substrateis used as a substrate for fabricating the electronic devices.Particularly, almost all of the transistor fabrications take the siliconsubstrate as the substrate in fabrication. However, the siliconsubstrate is a rigid substrate, and therefore the device being formed isalso a rigid device, without being flexible. The electronic product isthen not bent.

As the technology is continuously developed, some electronic devices canbe formed from organic material. For example, the technology about theorganic thin film transistor (OTFT) has gradually been well developed.For the available organic materials, the materials are generally dividedinto two types, for example, material with small molecules, such aspentacene, or material with large molecules, such as polymer.

In comparing the OTFT with the conventional in-organic transistor, theOTFT can be fabricated under a relative low temperature, therefore thesubstrate can be selected from plastic or glass, which are light, thin,and cheap. In addition, the fabrication process for the OTFT is simpler,and can use the printing technology to directly pattern the organic thinfilm. This can decrease the number of masks being used and the vacuumdeposition equipments. Further, since the OTFT is suitable forfabrication with the plastic substrate and is compatible with theprocess of roll-to-roll, it is quite helpful to reduce the fabricationcost in the future.

In order to form device on the flexible substrate, it should be overcomeon the issues that the temperature and stress may cause deformation onthe substrate and then occurrence of misalignment. Some conventionalissues are described as follows.

FIGS. 1A-1C are cross-sectional views, schematically illustrating theconventional fabrication process for the OTFT. In FIG. 1A, a rigidsubstrate 100 is provided to serve as the fabrication substrate. Inaddition, a flexible substrate 104 is adhered to the rigid substrate 100by an adhesive layer 102. The flexible substrate 104 is used forfabricating devices thereon.

Then, in FIG. 1B, a device structure, such as an OTFT, is to be formedon the flexible substrate 104. The fabrication process includes, forexample, a gate electrode 108 is formed on the flexible substrate 104. Adielectric layer 106 is formed over the flexible substrate 104 andcovers the gate electrode 108.

It should be noted that since the fabrication processes are performedunder a temperature. For example, all of the material layers, includingthe adhesive layer 102, may cause a bending, such as bending up as shownin FIG. 1B, due to difference of the thermal expansion coefficient. As aresult, the requirement of alignment in fabrication device may have themisalignment for the position of the gate electrode 108.

Further in FIG. 1C, when the flexible substrate 104 is stripped from therigid substrate 100, due to the adhering force from the adhesive layer102, the flexible substrate 104 is not easy to be stripped, and it needsto apply a stress on it, so as to be stripped. In addition, since theadhesive layer 102 in the fabrication process is still under thetemperature of about 200° C., and the adhesive material could betransformed and cured into different material, and then a residue 102 amay remain on the back of the flexible substrate 104. This would causethe poor quality of the device, or even damage the device. Moreover, theadhesive material is necessary to be coated and then adhered to therigid substrate, the planarity of the substrate cannot be easilycontrolled, and the fabrication processes are complicate. The poorplanarity of the substrate may also cause the issue of misalignment.

For another conventional technology is shown in FIGS. 2A-2C. ReferringFIG. 2A, in order to reduce the amount of use for the adhesive material,the adhering tapes 116 are only on the four corners, for adhering theflexible substrate 104. As a result, a space gap 118 exists between theflexible substrate 104 and the rigid substrate 104. FIG. 2B is a topview in FIG. 2A. The adhering tapes 116 are on the four corners of theflexible substrate 104.

In FIG. 2C, the subsequent fabricating processes for the OTFT include,for example, forming the gate electrode 122, the dielectric layer 104,source/drain regions 124 and 126, and the channel layer 128. Thisconventional method can simplify the process of stripping the flexiblesubstrate 104. However, since the issues about the thermal expansioncoefficients for the flexible substrate and the rigid substrate beingdifferent severely exits, it cause the misalignment problems on thedevice being fabricated.

In above considerations, the conventional technology still does notpropose the proper flexible substrate 104 for fabricating the devicethereon.

SUMMARY OF THE INVENTION

The invention provides a method for fabricating a device with flexiblesubstrate, at least allowing the flexible substrate to be formed on therigid substrate with planarity. In addition, the bending deformation forthe flexible substrate under the thermal environment of the processescan be effectively reduced, so as to improve the alignment for thedevice. Further still, when the device is accomplished in fabrication,the device can be sassily stripped from the rigid substrate withreduction of the residual material.

The invention provides a method for fabricating a device with flexiblesubstrate including providing a rigid substrate. Then, a flexiblesubstrate layer is directly formed on the rigid substrate, wherein theflexible substrate layer fully contacts the rigid substrate and acontact interface is formed. A device structure is formed on theflexible substrate layer.

In accordance with another embodiment from foregoing descriptions, astep for stripping the flexible substrate from the rigid substrateincluding dipping the flexible substrate and the rigid substrate in aliquid, in which the liquid has the capability to release the contactinterface.

According to another embodiment, the liquid can be water, and a dippingcondition includes dipping for a preset time period under a temperature.

Alternatively, the invention also provides a method for fabricating adevice with flexible substrate including providing a rigid substrate.Then, an interfacing layer can be formed on the rigid substrate and thenthe flexible substrate layer is directly formed on the interfacinglayer. The flexible substrate fully contacts the interfacing layer. Adevice structure is formed on the flexible substrate.

In accordance with another embodiment, it further comprises directlystripping the flexible substrate from the interfacing layer, wherein theinterfacing layer has a composition recipe, allowing the interfacinglayer to be stripped away substantially without the stress.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIGS. 1A-1C are cross-sectional views, schematically illustrating oneconventional fabrication process for the OTFT.

FIGS. 2A-2C are drawings, schematically illustrating anotherconventional fabrication process for the OTFT.

FIGS. 3A-3C are cross-sectional views, schematically illustrating thefabrication processes for the OTFT, according to an embodiment of thepresent invention.

FIGS. 4A-4C are cross-sectional views, schematically illustrating thefabrication processes for the OTFT, according to another embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method for fabricating a device withflexible substrate, and can have the flexible substrate being planarlyformed on the rigid substrate, so that the bending phenomenon on theflexible substrate under the thermal environment in processes can beeffectively reduced, and the precise position of the device can beimproved. In addition, when the device is accomplished in fabrication,the device can be easily stripped from the rigid substrate withreduction of the residual material. Some embodiments are provided as theexamples for descriptions but the present invention is not limited tothe embodiments.

FIGS. 3A-3C are cross-sectional views, schematically illustrating thefabrication processes for the OTFT, according to an embodiment of thepresent invention. In FIG. 3A, a rigid substrate 300 is provided toserve as a holding base. Material for the rigid substrate 300 can be,for example, glass, quartz, or silicon wafer. Then, a flexible substrate302 is directly formed on the rigid substrate 300. The flexiblesubstrate 302 serves as a substrate, on which a subsequent devicestructure can be formed. The flexible substrate 302 can be, for example,a substrate with large molecules or a substrate with small molecules, amixed substrate from inorganic and organic materials, or even a glasssubstrate with a thickness of about less than 0.2 mm. In addition, theflexible substrate 302 can be formed by coating process, such as diecoating or table coating. After the flexible substrate 302 is formed, itcan fully contact with the rigid substrate 300 to form a contactinterface 306. This contact interface 306 is helpful for the strippingthe flexible substrate 302. The features will be described layer.

In FIG. 3B, a device structure layer 304 is formed on the flexiblesubstrate 302. The device structure layer 304 can be the organic devicestructure or inorganic device structure. The device can include theusual electronic device, or even can include the non-electronicmechanical structure. The present invention is suitable for use in anystructure, which uses the flexible substrate as the structure base. Inaddition, the device structure layer 304 usually further formed with aprotection layer at bottom. The protection layer can be, for example, ahard coating layer for resisting water or a gas barrier layer. Theprotection layer is, for example, disposed between the actual device andthe flexible substrate 302. Further, for example, the device structurelayer 304 can include inorganic semiconductor device structure, organicsemiconductor device structure, organic circuit structure, or inorganiccircuit structure. The organic semiconductor device structure can be,for example, the OTFT, which can be formed under the process like FIG.1C. The dielectric layer 106 may have the dielectric constant aboutgreater than 3, and can be organic material or inorganic material. Thesource/drain regions 110, 112 and the channel layer 114 can be formed onthe dielectric layer 106. The material for the source/drain regions 110,112 and the channel layer 114 can be, for example, metal, conductivepolymer material, or conductive material mixed from organic andinorganic materials.

In other words, the present invention is not limited to what the devicestructure is formed on the substrate 302. However, any proper structure,which needs the flexible substrate 302 to serve as the structure base,can be use the present invention. Therefore, the detail for the devicestructure 304 is not further described, and can be understood by theordinary skilled artisans. The features of the present invention arecontinuously described.

The flexible substrate 302 of the present invention is directly formedon the rigid substrate 300, and therefore has improved planarity, whichis useful for device alignment. In addition, in order to easily stripthe flexible substrate 302 in subsequence process, the material of theflexible substrate is properly selected. In the preferred embodiment ofthe present invention, the polymer such as polyimide (PI)

poly(dimethylsiloxane) (PMDS)

PES

PEN

PET

PC and these derivatives are used. The polyimide can be directly formedon the rigid substrate 300 by a coated process. The polyimide can form acontact interface 306 with the rigid substrate 300 in substantiallynon-adhesive contact.

In FIG. 3C, when the device structure layer 304 is accomplished, thedevice with the flexible substrate 302 is necessary to be stripped fromthe rigid substrate 300. Due to existence of the contact interface 306,the present invention can perform the stripping process under asubstantial non-stress state. For example, the rigid substrate 300 isdipped into a liquid 308. By using the chemical phenomenon, such ashydrophobic property to water, the device on the flexible substrate 302can be stripped from the rigid substrate 300. Taking the polyimide asthe example, the liquid can be, for example, the water. In order toenhance the stripping effect, the liquid 308 can be heated to atemperature. Thus, after dipping for a few minutes, the flexiblesubstrate 302 can be stripped substantially without stress. Further, theflexible substrate 302 does not have the residual material.

In addition, with the same principle as described above, somemodification can be made, as shown in FIGS. 4A-4C. In FIG. 4A, aninterfacing layer 400 can be first formed on the rigid substrate 300.The thickness of the interfacing layer 400 is not limited, andpreferably is smaller than the rigid substrate. Then, the flexiblesubstrate 402 can be on the interfacing layer 400 by the same method aspreviously described. In the embodiment, the interfacing layer 400 is,for example, a thin polyimide (PI), and the material for the flexiblesubstrate 402, in accordance with the PI material, preferably ispoly(dimethylsiloxane (PMDS), for example. Due to the proper selectionon the material, a contact interface 406 can be formed, as shown in FIG.4B.

In FIG. 4B, the device structure layer 404 is formed on the flexiblesubstrate 402, and is similar to the device structure layer 304 in FIG.3B, and can be the device structure to be formed on the flexiblesubstrate 402. The descriptions about this part are omitted. However,the remarkable thing is the contact interface 406 produced by theflexible substrate 402 and the interfacing layer 400. Afterverification, if material for the flexible substrate 402 is PMDS, andcomposition of the PMDS has a recipe, then the adhering capability atthe contact interface can be controlled to a proper level withoutaffecting the formation of the subsequent device. Also and, the adheringcapability does cause the flexible substrate 402 to be strongly adheredto the interfacing layer 400. Remarkably, the foregoing selection onmaterial is just an example, and the present invention is not limited tothe specific material. The material with the foregoing interfacingfunction can be used in the present invention to serve as the flexiblesubstrate for fabricating device thereon.

In FIG. 4C, due to the foregoing properties of the present invention,after the device structure layer 404 is formed on the flexible substrate402, it can be directly stripped without introducing much stress,causing damage or residue on the device. Therefore, in the embodiment,according to the material selection for the interfacing layer 400 andthe flexible substrate 402, the flexible substrate 402 is allowed to bestripped substantially without stress. In comparing this embodiment withthe embodiment in FIG. 3C, even through the stripping mechanism islittle different, both are under the same design aspect. Some advantagescan be at least achieved as follows.

In the present invention, the flexible substrate can be directly formedon the rigid substrate. Thus, the planarity of the substrate can beimproved, and the bending deformation for the flexible substrate, causedby the difference of thermal expansion coefficients for the materials,can be effectively reduced. The conventional misalignment occurring atthe device structure can also be reduced.

In addition, since the present invention has the proper contactinterface between the flexible substrate and the rigid substrate,according to the property of the contact interface, the flexiblesubstrate can be stripped in a liquid or can be directly stripped,without causing over stress. As a result, the device is prevented fromdamage due to over bending and the residue can also be effectivelyreduced.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing descriptions, it is intended that the presentinvention covers modifications and variations of this invention if theyfall within the scope of the following claims and their equivalents.

1. A method for fabricating a flexible electronic device with flexiblesubstrate, comprising: providing a rigid substrate; directly forming aflexible substrate on the rigid substrate by a coating process of diecoating or table coating, wherein the flexible substrate is fullycontacting with the rigid substrate to form a contact interface; forminga device structure on the flexible substrate, wherein the devicestructure is integrated with the flexible substrate without separationas a part of the flexible electronic device; and stripping the flexiblesubstrate from the rigid substrate by dipping the flexible substrate andthe rigid substrate in a liquid, wherein the liquid has an ability torelease the contact interface, wherein the liquid is at a temperatureunder boiling water.
 2. The method of claim 1, wherein the liquid iswater, and a dipping condition comprises dipping under a temperature fora preset time period.
 3. The method of claim 1, wherein a material forthe flexible substrate is polymer.
 4. The method of claim 1, wherein amaterial for the flexible substrate is polyimide.
 5. The method of claim1, wherein the device structure comprises inorganic semiconductor devicestructure, organic semiconductor device structure, organic circuitstructure, or inorganic circuit structure.
 6. The method of claim 1,wherein the device structure comprises an organic thin film transistor.7. The method of claim 1, wherein the rigid substrate comprises glass,quartz, or silicon wafer.
 8. The method of claim 1, wherein the step offorming the device structure further comprises forming a protectionlayer between the device structure and the flexible substrate.